Fan

ABSTRACT

A fan comprises first and second rotor stages driven through a differential gear. The first stage is driven from the sun gear of the differential while the second stage is driven from the annulus gear of the differential. The planet carrier is driven from drive means. The invention is particularly applicable to gas turbine engines in which case the first stage of the fan may comprise a hub compressor and the drive means may comprise a gas turbine.

United States Patent 1 1 1111 3,729,957 Petrie et al. 1 1 May 1, 1973FAN [56] References Cited [75] Inventors: James Alexander Petrie,Littleover; UNITED STATES PATENTS Kenneth Edward Gem? 3,620,021 11/1971Lawrie ..60/226 R Fmdem both England 3,646,834 3 1972 Davis [73]Assignee: The Secretary of State for Defence, 3,673,802 7/1972 Krebs..60/226 Bmanmc M Govern FOREIGN PATENTS OR APPLICATIONS ment of theUnited Kingdom of Great Britain and Northern Ireland, 878,934 10/1961Great Britain ..60/226 R London, England [22] Filed; 21 1971 PrimaryExaminer-Douglas Hart Attorney-Cushman, Darby & Cushman [21] App]. No.:210,490

[57] ABSTRACT [30] Forelgn Apphcatlon Pnonty Data A fan comprises firstand second rotor stages driven Jan. 8, 1971 Great Britain ..975/71 hrugh a ifferential gear. The first stage is driven from the sun gear ofthe differential while the second [52] US. Cl. ..60/226 R, 60/268,60/39.16 C, stage is driven from the annulus gear of the dif- 74/665415/122 ferential. The planet carrier is driven from drive [51] Int. Cl...F02k 3/06, Fl6h 37/06 means The invention is particularly applicable mgas [58] Field of Search ..60/226 R, 268, 39.16 C;

turbine engines in which case the first stage of the fan may comprise ahub compressor and the drive means may comprise a gas turbine.

9 Claims, 2 Drawing Figures j Patented May 1 1'973 3,729,957

2 Sheets-Sheet J.

Patefited May 1, 1973 3,729,957

2 Sheets-Sheet 2 a z Z 30 2 -34 l6 FAN This invention relates to a fanwhich is particularly but not exclusively useful in a gas turbineengine.

Fans having large capacity are useful in a number of applications andparticularly in high by-passratio gas turbine engines. To produce thehigh capacity it has been the practice to increase the overall diameterof the fans, while to reduce complications entailed with very large hubsit has been the practice to make the hub of a fairly small size. Aproblem then arises in that to avoid the production of large amounts ofnoise the tip speed of the fan blades must be less than the speed ofsound; this therefore puts a limit on the rotational speed of the fanand consequently causes the inner sections of the fan blades to bemoving so slowly that it is difficult to cause them to operateeffectively. One solution which has been proposed is to provide anadditional fan stage whose diameter is considerably less than that ofthe main fan, this hub compressor being driven with the main fan or insome cases by a separate turbine.

The hub compressor then restores the efficiency of the central portionof the fan, but entails some complication in drive.

The present invention provides a fan having such a hub compressor andhaving a very simple drive which divides the torque available betweenthe main fan and the hub compressor.

According to the present invention a fan comprises a first and secondrotor stage in flow series and a differential gear comprising a sungear, a plurality of planet gears carried from a planet carrier, and anannulus gear, the first rotor stage being connected to the sun gear, thesecond rotor stage being drivingly connected to the annulus gear anddrive means connected to rotate the planet carrier.

Said first rotor stage may comprise a hub compressor and said secondstage may comprise a main rotor stage, the blades of the hub compressorextending over only the central portion of the main rotor stage.

In the case of a gas turbine engine the drive means will normallycomprise a turbine of the engine.

The hub compressor is preferably shrouded; thus the shroud may becarried from the main rotor stage and extend forwardly to encompass thehub compressor.

In a preferred embodiment the fan is mounted coaxially with a gasgenerator section so that the fan compresses air which provides by-passair and also supercharged inlet air to the gas generator. In ourpreferred case the gas generator is a two-shaft gas generator andcomprises a low pressure turbine which drives the planet carrier.

The invention will now be described merely by way of example withreference to the accompanying drawings in which:

FIG. 1 is a partly broken away view ofa gas turbine engine having a fanin accordance with the invention and FIG. 2 is an enlarged view of thefan portion of the engine ofFlG. 1.

FIG. 1 shows a gas turbine engine comprising .a gas generator section 10and a fan generally indicated at 11. The fan compresses air part ofwhich supercharges the gas generator 10 while the remainder passesbetween the gas generator and a fan cowl 12 to provide propulsivethrust. It will be seen that the gas generator is a two-shaft gasgenerator; that is it comprises intermediate pressure and high pressurecompressors l3 and 14 drivingly connected to intermediate and highpressure turbines 16 and 15 respectively. A third, low pressure turbine17 is provided and drives an LP shaft 18 which extends coaxially insidethe gas generator shafts to drive the fan.

The arrangement of the fan is best seen in FIG. 2. The fan comprises amain fan rotor 20 made up of a plurality of blades which carry part wayalong their extent a shroud ring 21. Within the shroud ring 21 andupstream of the main fan rotor 21]) there is a hub compressor 22 whichagain comprises a plurality of rotor blades which only extend over thecentral part of the main fan rotor 20.

The hub compressor 22 is driven from a shaft 23 which is mounted inbearings 24 and 25. The bearing 24 supports the shaft 23 from the shaft26 of the main fan 20, and this shaft is in turn supported by thebearing 27 from fixed structure of the engine. In addition to thesebearings, the shaft 26 supports bearings 29 and 30 whose purpose willbecome apparent below.

To drive the shafts 23 and 26, the shaft 23 is provided with an externalset of teeth .at 31 which form the sun wheel of an epicyclicdifferential gear. The shaft 26 is attached to an annulus gear 32 whoseinternal teeth form the annulus gear of the same differential. Aplurality of pinions 33 mesh between the sun gear 31 and annulus 32,these components being carried on a pinion carrier 34. The carrier isextended forwardly to mount within the bearing 29 mentioned above, whilethe rearward portion extends to form the LP shaft 18. This rearwardextension is supported in the bearing 30 and itself supports the bearing25 of the shaft 23.

Operation of the system is as follows:

Shaft 18 is driven by the LP turbine and consequently drives the planetcarrier 34. Rotation of this carrier causes the pinions to rotate aboutthe fan axis and causes equal driving loads to be exerted on the sunwheel 31 and the annulus gear 32. Because of the difference in thediameters of these wheels, a greater torque will be exerted on theannulus gear than on the sun wheel; consequently more power is passedinto the main fan rotor than into the hub compressor. This is thedesired splitting of work.

Theaerodynamics of the fan and hub compressor are arranged so that atdesigned speed for the turbine the fan will rotate at a fairly slowspeed, thus avoiding any danger of sonic or near sonic fan speeds whichwould produce noise. The hub compressor is arranged to rotateconsiderably faster, since with its relatively small diameter bladesthere is little chance of its blades going sonic. Since the hubcompressor rotates at a relatively high speed it can be reasonablyefficient over its radial extent; it therefore makes up for the relativeinefficiency of the central section of the fan blades. In fact the innerportion of the fan blades may be made simply as struts which perform nowork on the air which has been compressed by the hub compressor.

It will be appreciated that the sun gear, planet carrier and annulusgear all rotate in the same direction, the differential speed betweenthe sun and annulus gears being taken up by rotation of the pinions. Itwill be understood by those skilled in the art that the arrangement inwhich these gears rotate in the same sense produces considerably lessfriction loss than a gear in which components contra-rotate. Thus ourpresent arrangement reduces frictional losses to a sixth of aconventional epicyclic gear arrangement. Such a reduction is of thegreatest importance in applications where the transmitted power is veryhigh since frictional losses which appear as heat in the lubricatingfluid cause great difficulty in rejecting heat in sufficient quantities.

It will be' appreciated that this invention is particularly relevant tothe fans of gas turbine engines but can be applied to other fans,particularly propulsive fans which may be used for VTO application etc.In any of these cases it is only necessary to provide the drive in theform of a single shaft, the gear arrangement of the invention providingthe necessary splitting of power.

We claim:

1. A fan comprising a first and a second rotor stage in flow series anda differential gear comprising a sun gear, a plurality of planet gearscarried from a planet carrier, and an annulus gear, first connectionmeans by which the first rotor stage is connected to the sun gear,second connection means by which the second rotor stage is drivinglyconnected to the annulus gear and drive means connected to rotate theplanetcarrier.

2. A fan as claimed in claim 1 and in which said first rotor stagecomprises a bladed hub compressor, and

the second stage comprises a main bladed rotor stage, the blades of thehub compressor extending over only the central portion of the-main rotorstage.

3. A fan as claimed in claim 2 and in which there is a shroud round theblades of the hub compressor.

4. A fan as claimed in claim 3 and in which the hub compressor shroud iscarried from the main rotor stage and extends forwardly to encompass thehub compressor.

5. A fan as claimed in claim 1 and in which said drive means comprises agas turbine.

6. A fan as claimed in claim 5 and in which said fan drive gas turbineis driven by the exhaust gas of a gas generator.

7. A fan as claimed in claim 6 and in which said gas generator comprisesa gas turbine gas generator.

8. A fan as claimed in claim 7 and in which said gas generator has anair intake, the rotors being mounted coaxially ahead of the intake sothat the fan compresses air which provides by-pass air and superchargedinlet air to the gas generator.

9. A fan as claimed in claim 8 and in which said gas turbine gasgenerator comprises a multi-shaft gas generator.

1. A fan comprising a first and a second rotor stage in flow series anda differential gear comprising a sun gear, a plurality of planet gearscarried from a planet carrier, and an annulus gear, first connectionmeans by which the first rotor stage is connected to the sun gear,second connection means by which the second rotor stage is drivinglyconnected to the annulus gear and drive means connected to rotate theplanet carrier.
 2. A fan as claimed in claim 1 and in which said firstrotor stage comprises a bladed hub compressor, and the second stagecomprises a main bladed rotor stage, the blades of the hub compressorextending over only the central portion of the main rotor stage.
 3. Afan as claimed in claim 2 and in which there is a shroud round theblades of the hub compressor.
 4. A fan as claimed in claim 3 and inwhich the hub compressor shroud is carried from the main rotor stage andextends forwardly to encompass the hub compressor.
 5. A fan as claimedin claim 1 and in which said drive means comprises a gas turbine.
 6. Afan as claimed in claim 5 and in which said fan drive gas turbine isdriven by the exhaust gas of a gas generator.
 7. A fan as claimed inclaim 6 and in which said gas generator comprises a gas turbine gasgenerator.
 8. A fan as claimed in claim 7 and in which said gasgenerator has an air intake, the rotors being mounted coaxially ahead ofthe intake so that the fan compresses air which provides by-pass air andsupercharged inlet air to the gas generator.
 9. A fan as claimed inclaim 8 and in which said gas turbine gas generator comprises amulti-shaft gas generator.